1. Field of the Invention
This invention generally relates to a rotary bearing assembly and in particular to a rolling contact type rotary bearing assembly including a pair of inner and outer rings and a plurality of rolling members interposed between the inner and outer rings.
2. Description of the Prior Art
A rotary bearing assembly having a plurality of rollers as the rolling members is disclosed in the U.S. Pat. No. 4,606,654 which is assigned to the assignee of this application and which is hereby incorporated by reference. In the structure disclosed in this U.S. Pat. No. 4,606,654, an insertion hole for inserting a plurality of rollers into a space between a pair of inner and outer rings is provided in the outer ring and the insertion hole has a shape which is slightly larger than the diameter of the roller at its inlet and which gradually flares out toward the space between the inner and outer rings. In this structure, the outer ring can be made thinner without imparing its strength and structural integrity and the bearing assembly can be made smaller in size. However, in this structure, since a gap is defined between a plug inserted into the insertion hole after feeding a required number of rollers into the space between the outer and inner rings and the outer ring because of the flared out shape of the insertion hole, the guide surface of the outer ring along which the rollers role is not smooth so that the rollers tend to strike against the tip end of the plug when they roll. In addition, since the insertion hole has a flared-out structure, difficulty is encountered in manufacture.
In order to cope with this situation, there has been proposed an improved crossed roller bearing assembly having an insertion hole as disclosed in the U.S. patent application No. 07/329,928, which was filed on Mar. 29, 1989, now U.S. Pat. No. 4,961,653. and which is assigned to the assignee of this application and is hereby incorporated by reference. In accordance with the teachings of this U.S. Patent Application, a plug is snugly fitted into an insertion hole provided in either one of inner and outer rings of a bearing assembly such that the end of the plug is located slightly short of a V-shaped guide surface of the ring in which the insertion hole is provided. Such a structure is no doubt advantageous in reducing the rolling resistance since none of the rollers does not come into direct engagement with the tip end of the plug. However, when such a bearing assembly was used in a large-sized robot or the rotating table of a crane, it was found that an relatively increased rolling resistance often resulted. In addition, when such a bearing assembly was used in a high precision machine, appreciable fluctuations occurred in the rotating torque. Besides, there was some difficulty in manufacturing such a bearing assembly, particularly in setting the tip end of a plug slightly short of the guide surface of the ring.